Production of pith free paper pulp from bagasse



H. D. STUCK Juhe 17, 1958 PRODUCTION OF PITH FREE PAPER PULP FROM BAGASSE Filed Sept. 27, 1952 INVENTOR. HAROLD D. STUCK ATTORNEYS 2,839,398 Patented June 17, 1958 PRODUCTION OF PITH FREE PAPER PULP FROM BAGASSE Harold D. Stuck, Andover, Mass, assignor to Process Evaluation and Development Corporation, New York, N. Y., a corporation of Delaware Application September 27, 1952, Serial No. 311,925 4 Claims. (Cl. 92--9) This invention relates to the manufacture of paper grade pulp from bagasse and the stalks of similar pithy plants of the family Graminae, and has for its primary object the rapid production of the maximum high grade pith free pulp from such materials.

The production of paper from bagasse has long been the subject of investigation, but the processes developed have all been subject to the difficulties inherent in the separation of pith from the fibers, the expense of which has placed such pulp at a competitive disadvantage with other pulps of the same quality. Commercial production of pulp from bagasse requires first an efficient and inexpensive process of removing the pith from the fiber bundles without degradation or weakening of the fibers and secondly a digestion of the fibers to a pulp of the highest obtainable quality, at a minimum expense. Yields from the material are such that the maximum quantity of highest quality pulp is economic necessity.

The present invention provides rapid and efiicient pith removal during which the fiber bundles are conditioned for a subsequent prescribed rapid digestion into chemical grade pulp. The entire process requires only a fraction of an hour for complete conversion of bagasse to pulp, and the pulp produced is high in alpha cellulose with controllably low amounts of hemicellulose, pentosans and lignin, and is of extreme whiteness Without having undergone a subsequent bleaching operation. The savings resulting from complete, rapid and inexpensive pith removal combined With the generally higher quality and quantity of the pulp produced by this invention now make the utilization of bagasse for pulp, a practical endeavor.

The process of this invention consists essentially of two. i 9

main operations, a pretreatment to separate the pith and condition the fiber bundles for rapid and thorough digestion, and a digestion phase employing novel digesting solutions in a digestion treatment accelerated by heat and pressure. geously combined as successive steps or in a continuous process, each could be practiced independently of the other, the pretreatment where it is not desired to process the clean pith-free fibers further to produce pulp, or be briquetted for more compact cooking, and the digestion phase Where pith-free fibers from other sources are available.

The pretreatment operation consists in 1th treatment of the bagasse with a hot aqueous solution of heat resistant carbohydrate-digesting or protein-digesting enzymes, accompanied or followed by violent agitation of a slurry of bagasse to loosen the pith cells from the fiber bundles. The pith cells are thereafter removed from the fiber Although the two operations are advantabundles as by washing the bagasse solids on a screen of mesh dimensions adapted to hold the fibers and pass the pith.

Enzymes which have been found suitable for the pretreatment include those which are stable in the temperature range of 6il75 C., and active on cellulose or hemicellulose, on starches, or on proteins, and mixtures thereof, and should be present in the pretreating solution in a concentration of at least about 1.0% by weight. That both carbohydrate active enzymes and protein active enzymes are effective in this process to facilitate loosening of the pith cells is believed accounted for by the fact that the cementitious material binding the pith cells to the fiber bundles is partly carbohydrate and partly protein. The enzyme solution is mixed with the dry bagasse in sufiicient quantity to cover it completely, and is maintained in contact with the bagasse until the pith is loosened and the fibers softened (usually 10-15 minutes) at a temperature of about 75 C. The bagasse is then violently agitated either while in contact with the enzyme solution, or preferably after draining oil the enzyme solution for reuse and adding hot (about 50 C.) water to the bagasse to form an aqueous slurry. The bagasse is thereafter drained and Washed free of the detached pith cells on a suitable screen. During the pretreatment the pith is loosened'and detached so that small, weak fibers Within it are easily separated, and the fibers recovered are bright, strong and free of pith, silica, wax, iron and other impurities.

An alternative pretreatment requiring a longer time,

- vat with an aqueous solution containing at least about 3 percent of starch and cellulose. active enzymes (for instance malt diastase) and at least about 3 per-cent of ry yeast, both quantities being based on the dry weight of the bagasse. The bagasse is held submerged in the solution for about twenty-four hours at a temperature be tween about 20 and 33 C., after which the solution is drained off. The bagasse is .then violently agitated for about three minutes in a slurry of hot water (about 50 C.), and then screened to separate the pith cells which have been completely detached from the fiber bundles, as well as pith cells loosened so that all fiber can be easily removed. This enzyme treatment practically entirely removes all the wax, silica and iron, which are not removed by prior methods. It also separates the weak pith fibers from the pith so that pith can be completely segregated, as such. i

After pretreatment to separate and remove the pith, without in ury to the fiber bundles, the fiber bundles are digested to the desired paper grade of pulp. In the cligestion phase of this invention, the pith-free fiber bundles are treated consecutively with two solutions at elevated temperature and pressure, then subjected to a sudderit release of pressure terminating the second treatment, and explosively expanding the fiber bundles to disintegrate them to pulp. The first solution is a diluted standard kraft type solution of about one-third ordinary strength (that is limited to about 3% NaOH and 1.5% Na s by weight) containing about 25% by weight of added sodium peroxide and about O.2l.0% by weight of added ammonium nitrate. The bagasse is submerged in this solution for at least about four minutes under a saturated steam pressure of about 150 p. s. i. applied either di rectly or indirectly to the solution. The solution unadsorbed by the fibers is then drained off, and the second solution, containing in water about l.02.5% by weight of sodium pyrophosphate peroxide (Na P O7.2l-l O and preferably also about 0.41.2% by weight of sodium hexa metaphosphate (NaPO is added to cover the bagasse fibers, and permeate through the cook, and is maintained in contact with the fibers for at least about two minutes under a saturated steam pressure of about 175 p. s. i. ap-

plied directly or indirectly to the soluticn'and fibers. solution is then drained off, and immediately followed by a sudden release of the pressure to cause an explosive expansion of the wet fiber bundles to produce pulp, which is then washed and screened to prepare it for beating and paper making.

Various combinations and adjustments of this solution, as to chemical content and percentages can be made to compensate for physical and chemical differences in lot to lot variations in raw material, and desired end product.

The following example describes in detail the best procedure I have found for practicing my invention. In the accompanying drawings:

Fig. 1 is a schematic diagram of apparatus for carrying out-the pretreatment steps of the process, and

Fig. 2 is a cross section view of apparatus for carrying out the digestion steps of the process.

Suitable apparatus for carrying out the pretreatment operation of this invention is shown in Fig. 1, and con- 9 sists mainly of a steam jacketedreactor 10 having a propeller-mixer 11, an agitator 12 equipped with a high speed mixer 13, a gyratory screen 14.for draining the solids from the slurry from the agitator and a classifying screen 16. The several units are mounted forgravity flow from one unit to the next, and are equipped for the recycle of all or part of the various solutions encountered in the process.-

T he reactor 10 is a generally cylindrical jacketed vessel having an open conical bottom through the wall of which is mounted the mixer 11. Near the lower end of the conical bottom is a band'of perforations 20 leading to an annular channel 22 which connects with the inlet of a pump 26 the outlet of which leads through a control valve 28 back to the reactor vessel, into which also leads a make-up feed conduit 23. The open bottom connects with a conduit24 leading through a valve 25 to the agitator 12.

The agitator 12 consists of a slightly downwardly tapering vessel" having a closed-bottom provided with a discharge opening in which isremovably mounted a valve plug 26. A pair of high spee'd'mixing propellers 13 and 13 are mounted'near the bottom of the vessel on a vertical shaft The agitator 12 drains into an'elongated tank 28 divided by a partition 29 intoa drainage reservoir 30 situated beneath theagitator 12 and a pith collecting connected a filling conduit 44, and a drain connection 46, covered by a foraminous trap 48. A steam line 42 connects into the jacketed space to provide proper heating of the contents. A cover 50, bolted to a flange 51 at the top of the vessel, and provided with a quick opening valve 52, closes the vessel while providing for quick release of the pressure therein. A venting valve 53, is also provided in the cover to allow air to be vented from the vessel.

In the process of this invention as typically carried out the bagasse and an aqueous solution containing about 1.5% by weight of the enzyme are fed continuously into the reactor 10 in the ratio of 600 gals. of solution to 1000 lbs. of dry bagasse. Suitable commercial enzyme preparations that have been used include:

Rhozyme DX, manufactured by Rohm & Haas Co., Philadelphia, Pa, and described by the manufacturer as a diastatic enzyme preparation which is characterized by its strong starch-liquefying (alpha-amylase) activity.

19 AP, manufactured by Rohm & Haas Co., Philadelphia, Pa., and described as a mixture of enzyme systems including cellulase, hemicellulase, gumase and maltase and having hydrolytic activity on cellulose, hemi-cellulose, gums and matose.

Serizyme, manufactured by Wallerstein Company, New York, N. Y., and described as a proteolytic enzyme preparation.

Steam is admitted to the steam jacket of the reactor 10 to maintain the temperature of the mixture at about 75 C., and the discharge valve 25 is adjusted to allow the mixture to pass through the reactor in about fifteen minutes. Agitation and thorough mixing of the contents are maintained by the mixer 11.

As the mixture discharges from the bottom of the reactor, about 60-75 of the enzyme solution is withdrawn through the perforations 20 and annular channel 22, and

recycled into the reactor through the pump 26, and additional make-up enzyme'solution is added through the make-up conduit 23 to maintain the proper proportions reservoir 31. An inclined fine rn'esh-screen'or screens 14 is mounted between the drainage reservoir 31 and the agitator 12, with its lower edge leading into the upper end of an inclined rotary screen classifier 16 mounted for rotation with its lower end just partly submerged in the pith collecting reservoir 31.' Shower tubes 32 and 33 are provided for spraying both the exterior and interior of the rotary screen classifier 16.

The drainage reservoir 30 is provided with a drain leading to the inlet of a pump 34 and the outlet of which discharges into the agitator 12, and both reservoirs are provided with overflow drains 35 and 35 which maintain constant liquid levels.

The pith-free fiber bundles discharged from the lower 7 end of the screen classifier 16 are collected on an elevator The digestor, shown in Fig. 2, consists of a steam jacketed'vertical" cylindrical vessel 40, into which are of enzyme solution as additional bagasse is added.

The mixture then passes into the agitator 12, togetherwith suflicient hot water to form a thin slurry, conveniently recycled water subsequently drained from the effluent from the agitator and heated to about 50 C., in an amount to provide a slurry ratio of about 1000 gals. of

solution per 1000 lbs. of dry bagasse. The discharge from the agitator is controlled through the valve plug 26 to hold the mixture in the agitator for about 2 to 5 minutes, during which time the contents are violently.

agitated to loosen the pith cells by the high speed propeller mixer 13.

From the agitator 12 the mixture flows onto the gymtory screen 14 which filters out the solids and delivers them to the rotary screen classifier 16, while the liquid fraction drains into the drainage reservoir 30 from which the required fraction to be returned to the agitator is withdrawn by the pump 34 and heated by conventional" means.

In the rotary screen classifier the mixture is copiously showered with water from both inside and outside the rotating screen from the shower tubes 32 and 33. The

pith is thereby washed through the meshes into' the pith collecting reservoir 31, while pith-free fiber bundles are Washed along the inclined screen and discharged from its lower end onto the elevator 36 and carried to the digestor.

In digesting the fiber bundles to convert them to pulp, the steam jacketed vessel 40 is heated by steam to about 215 C., filled with drained wet pith-free fibers, and closed by the cover 50, the valve 52 therein also being closed. Saturated steam under a pressure of 25-50 p. s. i. g. is induced by raising external chamber steam pressure through the steam line 42, and the first digesting solution is pumped in through the filling conduit 44,while air is vented from the vessel through the venting valve 53.

A typical first solution has the following composition (by weight) Standard kraft solution containing in water 34%.

(by weight).

NaOH pereent NnzCOa. dd... 1.5 NazS04 -.do- 0.83 Wetting agent, --do 0.25

Nonic 218, sold by Sharples Chemicals, Inc., Philadelphia, Pa., and described as polyethylene glycol tertdodeeylthioether, or Triton X100, sold by Rohm dz Haas 00., Philadelphia, Pa., and described as an alkyl aryl polyether alcohol.

Sodium peroxide solution containing in water (by weight).

N820: -percent 5.

Stabilizer, e. g. Sunolox, sold by Pennsylvania Salt Manufacturing Co. as a peroxide bath adjuvant to stabilize peroxide solutions, believed to be an alkaline earth polyphosphate pereent. 0.5 Ammonium nitrate solution containing About 12 fluid oz. per lb. in water (by weight). of dry fibers or about NH4NO3 percent.. 3 13%.

When the vessel is full of the first solution, and the fibers submerged therein, the steam pressure applied through the steam line 42 is raised rapidly, preferably in less than two minutes, to about 150 p. s. i. g., and held there for about four minutes. The vessel is then drained of solution unadsorbed by the fibers through the drain connection 46, and the second solution is introduced through the feed conduit 44 to fill the vessel.

The second solution is typically an aqueous solution of the following composition (by weight) Percent Sodium pyrophosphate peroxide 1.66 Stabilizer, e. g. Sunolox 0.5 Sodium hexametaphosphate (NaPO 0.8

The steam pressure is then raised rapidly, preferably in less than one minute to about 175 p. s. i. g. and maintained for about two minutes. About 25% of the total liquid is then drained off, with the steam pressure still maintained at about 175 p. s. i. g., and the quick opening valve 52 is opened suddenly, preferably in less than $4 of a second, whereupon the fibers are blown from the vessel into the open air and expanded into separate pulp fibers, which are then collected, washed and screened and further processed in ordinary paper making operations.

The pulp produced by this invention is of maximum yield of high quality and light color, a typical analysis being:

Alpha cellulose ..-percent 85-96 Hemi-cellulose do- 3-10 Pentosans do- 1-6 Lignin do 1-10 Permanganate number 2.5-8 Cuprammonium viscosity 6-30 Moreover, a bleaching operation subsequent to pulping is entirely unnecessary, an advantage representing a substantial economy, and the beating time may frequently be as much as 65% below that of other pulps. An important advantage will also be observed to lie in the extreme rapidity of the process, wherein bagasse may be converted to pith-free pulp in about forty minutes, thus greatly reducing the size requirements of equipment, Water consumption, material handling and total overall costs.

A comparison of pulp produced by the present invention with a conventional bagasse pulp is given in Table I.

It will be understood that this invention is not limited to the details of the preferred procedure described above, and that modifications thereof may be made without departing from its scope. The apparatus described in the application of Clarence Birdseye, Serial No. 285,844, filed May 3, 1952, may be used for agitation and pith removal in the pretreatment phase of the process of this invention, and the apparatus described in my joint application with Birdseye, Serial No. 260,352, filed December 7, 1951, now Patent Number 2,771,361 may be used in the digestion phase.

Having thus disclosed my invention and described in detail a preferred example thereof, I claim and desire to secure by Letters Patent:

1. The process of converting bagasse or the like to pithfree uniform high grade bright colored paper pulp comprising the steps of: treating the bagasse in an aqueous solution of enzymes selected from the group consisting of carbohydrate-active enzymes and protein-active enzymes to loosen the pith cells from the fiber bundles; agitating the bagasse violently in an aqueous slurry to detach the pith cells from the fiber bundles; digesting the fiber bundles first in a kraft-type solution containing by weight about 3% NaOH and 1.5% Na s and comprising additionally by weight about 2-5% sodium peroxide with a stabilizer therefor and about 0.2-1.0% ammonium nitrate, under a saturated steam pressure of about p. s. i. g.; then draining olf solution unadsorbed by the fibers and adding an aqueous solution comprising by weight about 1.0-2.5% sodium pyrophosphate peroxide, continuing the digestion under a saturated steam pressure of about p. s. i. g.; and terminating the second digestion by suddenly releasing the pressure to cause an explosive expansion of the fiber bundles to pulp.

2. In the process of converting bagasse or the like to pith-free uniform high grade bright colored paper pulp the method of removing the pith from the fiber bundles comprising: treating the bagasse in an aqueous solution of enzymes selected from the group consisting of carbohydrate-active enzymes stable at a temperature between 6075 C., and protein-active enzymes stable at a tem perature between 60-75 C. for 10-15 minutes at a temperature between about 60-75 C. to loosen the pith cells from the fiber bundles; agitating the bagasse violently in an aqueous slurry to detach the pith cells from the fiber bundles; and separating the free pith cells from the fiber bundles.

3. In the process of converting bagasse or the like to pith-free uniform high grade, bright colored paper pulp the method of digesting pith-free fiber bundles to pulp comprising contacting the fiber bundles in a Kraft-type solution containing by weight about 3% NaOH and 1.5% Na s and comprising additionally by weight about 2-5% sodium peroxide with a stabilizer therefor, about 0.2- 1.0% ammonium nitrate and a nonionic wetting agent, under a saturated steam pressure of about 150 p. s. i. g. for about 4 minutes; then draining off solution unadsorbed by the fibers and adding an aqueous solution comprising by weight about 1.0-2.5 sodium pyrophosphate peroxide and continuing the digestion under a saturated steam pressure of about 175 p. s. i. g.; and terminating the second 2, sewa e? 7. digestion by suddenly Ieleasi'iig 'the pressure to cause an explosive expansion of the fiber bundles to pulp. H

4. The process of converting bagasse or the like to pith-fr'eeuniform high grade, bright colored paper pulp comprising the 'stepsof: treating the bagasse in an aqueous solution of enzymes selected from the groups consisting of .carbohydrateractive. enzymes stable at a temperature between 60-75 O, and protein-active enzymes stable ata temperature-between 6()75 C., at a temperatureof about 60-75 F. for at least 1Q--'15'minujtes'to'loosen-the pith cells from the fiber bundles; agitating the bagasse violently in an aqueous slurry todetach' the pith'cells from the fiber bundles; separating the free pith cells from the fiber bundles; digesting the pith free fiber bundles in a kratt-type' solution of about one-third ordinarystre'ngth and comprising additionally byweight about 2-5 s0- dium peroxide with-a stabilizer therefor, about O.2-'1.0%'-

ammonium nitrate and a non-ionic wetting agent under a saturatedsteain pressure of about 150 p. s. i. g. for'about 4 minutes; then draining oft solutio'n'unadsorbed by the fibers and adding an aqueous solution" comprising -by weighti'abou-t 1.0- 2-:5 'sodium' pyrophosphate peroxide and continuing the digestion under a saturated steam pressure of about 175 p. s. i. g.; and terminating the second digestion by suddenlyreleasing the pressure to cause an- .explosive expansion of the fiber bundles to pulp.

References Citedin the file of this patent UNITED STATES PATENTS 

1. THE PROCESS OF CONVERTING BAGASSE OR THE LIKE TO PITHFREE UNIFORM HIGH GRADE BRIGHT COLORED PAPER PULP COMPRISING THE STEPS OF: TREATING THE BAGASSE IN AN AQUEOUS SOLUTION OF ENZYMES SELECTED FROM THE GROUP CONSISTING OF CARBOHYDRATE-ACTIVE ENZYMES AND PROTEIN-ACTIVE ENZYMES TO LOOSEN THE PITH CELLS FROM THE FIBER BUNDLES, AGITATING THE BAGASSE VIOLENTLY IN AN AQUEOUS SLURRY TO DETACH THE PITCH CELLS FROM THE FIBER BUNDLES, DIGESTING THE FIBER BUNDLES FIRST IN A KRAFT-TYPE SOLUTION CONTAINING BY WEIGHT ABOUT 3% NAOH AND 1.5% NA2S AND COMPRISING ADDITIONALLY BY WEIGHT ABOUT 2-5% SODIUM PEROXIDE WITH A STABILIZER THEREFOR AND ABOUT 0.2-1.0% AMMONIUM NITRATE, UNDER A SATURATED STREAM PRESSURE OF ABOUT 150 P. S. I. G., THEN DRAINING OFF SOLUTION UNADSORBED BY THE FIBERS AND ADDING AN AQUEOUS SOLUTION COMPRISING BY WEIGHT ABOUT 1.0%-2.5% SODIUM PYROPHOSPHATE PEROXIDE, CONTAINUING THE DIGESTION UNDER A SATURATED STREAM PRESSURE OF ABOUT 175 P. S. I. G., AND TERMINATING THE SECOND DIGESTION BY SUDDENLY RELEASING THE PRESSURE TO CAUSE AN EXPLOSIVE EXPANSION OF THE FIBER BUNDLES TO PULP. 